General pathology · Hemodynamic disorders
Fat, air and amniotic fluid embolism !
- Topic
Not every embolus is a clot: fat, gas bubbles, amniotic fluid, cholesterol crystals, bacteria and tumour can travel too.
Updated 2026-11-01
What it is
An embolus is any mass that travels in the blood and lodges far from where it started. Besides thrombi there are emboli of fat and marrow after fractures, of gas from air entering the veins or from sudden decompression, of amniotic fluid during childbirth, of cholesterol from atheromatous plaques, septic emboli from vegetations, and tumour emboli. Each has its typical setting and its own clinical picture.
Step by step
- Fat embolism: the fracture releases marrow fat into torn veins.
- The globules block lung capillaries and some pass into the systemic circulation.
- Released fatty acids injure the endothelium and activate platelets: edema, hemorrhages and thrombocytopenia.
- Amniotic fluid embolism: the fluid enters uterine veins through a tear in the membranes or the uterus.
- Its components trigger coagulation and an intense inflammatory response: hypoxemia, shock and DIC.
Emboli that are not thrombi
| Type | Setting | What is seen or caused |
|---|---|---|
| Fat and bone marrow | Femur or pelvic fracture, orthopaedic surgery, burns | Fat globules in lung and brain capillaries; petechiae |
| Gas (decompression, air) | Diving, unpressurised flight, central venous catheters | Bubbles that block vessels; femoral head necrosis in the long run |
| Amniotic fluid | Labour, caesarean section, right after delivery | Cardiorespiratory collapse, seizures and DIC |
| Cholesterol (atheroembolism) | Catheterisation or aortic surgery in severe atherosclerosis | Blue toes, kidney injury, cholesterol clefts |
| Septic | Infective endocarditis, infected thrombophlebitis | Infarcts that turn into abscesses |
| Tumour and foreign bodies | Invasive cancer; talc in injected drugs | Metastases; foreign-body granulomas in the lung |
Clinical notes
- Suspect fat embolism with hypoxemia, confusion and petechiae in the armpits and conjunctivae one to three days after a femur fracture.
- Amniotic fluid embolism is rare but carries a high maternal mortality.
Test yourself
Think of the answer, then tap the question to see it.
Which triad marks fat embolism syndrome?
Respiratory failure, neurological changes and petechiae, appearing one to three days after the fracture.
Which gas causes decompression sickness?
Nitrogen dissolved in blood and tissues, which forms bubbles when the surrounding pressure falls quickly.
What is found in the maternal lungs in amniotic fluid embolism?
Fetal squamous cells, lanugo hair, mucin and fat from the vernix inside the pulmonary microvasculature.
Why is fat not seen in a routine H&E section?
Because the processing solvents dissolve it; frozen sections and lipid stains are needed.
Related
- Pulmonary thromboembolism: where it comes from and what it does
- Systemic (arterial) thromboembolism
- Disseminated intravascular coagulation: how consumption causes both clots and bleeding
- Special stains in diagnosis: Congo red, Prussian blue, PAS, Ziehl–Neelsen, Gram
Related conditions
- Fat embolism syndrome
- Amniotic fluid embolism
- Atheroembolic renal disease (cholesterol crystal embolism)
- Decompression sickness and diving injuries
- Avascular necrosis of the femoral head
- Infective endocarditis
- Major trauma (polytrauma): ATLS primary survey
- Disseminated intravascular coagulation
Elsewhere in DurgiPedia
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Pulmonary embolus: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2025); Arterial embolism: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.